Retractable tail-lift for a vehicle

ABSTRACT

A retractable tail-lift for a vehicle comprises a lifting mechanism ( 30 ) for lifting and lowering a platform ( 50 ), and guiding rails ( 21 ) in which the lifting mechanism ( 30 ) with one vertical carriage ( 32 ) each is suspended and can be slidably displaced between a working position located behind the vehicle and a travelling position located below the vehicle, wherein each carriage ( 32 ) has a front guiding element ( 40   a ) with an upper sliding member ( 42   a ) and rear guiding element ( 40   b ) with a lower sliding member ( 42   b ). The front guiding element ( 40   a ) is attached from above onto the carriage ( 32 ) and is arrested on the carriage ( 32 ) at right angles to the direction of attachment, and the rear guiding element ( 40   b ) is attached from below onto the carriage ( 32 ) in an opening ( 32.3 ) of the carriage ( 32 ) and is arrested on the carriage ( 32 ) at right angles to the direction of attachment.

BACKGROUND OF THE INVENTION

A retractable tail-lift of this type is disclosed e.g. by the Hydfalt 3model range of the company Gerd Bär GmbH, Heilbronn.

Tail-lifts are mounted to lorries or trailers for loading and unloadingthem. Retractable tail-lifts are mounted to the chassis using a guidingmechanism and can be retracted completely under the body or chassisframe after folding the platform once or twice, such that they do notproject at any location to the rear beyond the body to prevent anydisturbance. Retractable tail-lifts of this type are used for vehicleswith interchangeable bodies and for all vehicles which must dock ontoloading/unloading regions of cold storage houses.

In the Hydfalt 3 model range, the guiding mechanism is formed by twoguiding rails in which the lifting mechanism with one vertical carriageeach is suspended, and can be slidably moved between the workingposition located behind the vehicle and the driving position locatedbelow the vehicle. Each carriage comprises a front guiding element withan upper sliding member which abuts on an upper guiding surface of theguiding rail, and a rear guiding element with a lower sliding memberwhich abuts on a lower guiding surface of the guiding rail. The guidanceis disposed inside the guiding rails to protect the guiding surfacesfrom dirt. The guiding rail may also be mounted at any location to thevehicle or to cross members, which facilitates dimensioning of theguiding rail. This technology also provides maintenance-free slidingguidance if the sliding partners are appropriately selected. Thesesliding guidances have the object to adopt the net weight of the liftingmechanism and the platform and slidingly transfer it to the guidingelement during folding and unfolding. The guiding elements also have theobject to assume horizontal guidance during forward and backwardmovement. The centrally acting displacement cylinder and the irregularfriction must simultaneously provide horizontal guidance. Theunfavorable leverages—the separation of the guiding elements and thecenter of gravity of the tail-lift—also produce large horizontal guidingforces. Since the sliding materials, which consist substantially ofplastic material or plastic composite material, are subjected to wear,the sliding members of the Hydfalt 3 model range are suspended on thecarriage to obtain even wear. Towards this end, the symmetric guidingconstruction has guiding elements of aluminium for the tension side aswell as the pressure side on both sides of the carriage plate. Thisguiding elements comprise chambers which are open towards the bottom forreceiving the sliding elements, and are commonly borne by a speciallydisposed bolt which penetrates through the carriage plate. Thisconstruction requires relatively high precision and expensive measuresto protect the support and bolt from rust. Guiding surface is wasted onthe pressure side of the carriage in the region of the carriage platethickness. With this construction, the forces are deviated through thebolt into the carriage plate, thereby producing a very large internalbore surface which necessitates great material solidity. The carriageplate thickness must nevertheless be excessively thick. Thisconventional construction is therefore technically very demanding andtherefore expensive.

SUMMARY OF THE INVENTION

Servicing of the inventive construction is extremely easy. Changing ofthe sliding members is very simple and requires no connecting means.Removal of the guiding elements, replacing the sliding members, andreinsertion are facilitated. Faults caused by untrained staff are almostimpossible. The same applies for initial assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the invention can be extracted from thedescription and the drawing. The features mentioned above and below maybe used individually or in arbitrary combination. The embodiment shownand described is not to be understood as exhaustive enumeration but hasexemplary character for describing the invention.

FIG. 1 shows a side view of the retractable tail-lift in its retractedtravelling position and in its extended working position;

FIG. 2 shows a carriage which can be displaced in a guiding rail, of theunderridable elevating platform of FIG. 1;

FIG. 3 shows a detailed view of the carriage of FIG. 2 in the region ofa front guiding element;

FIG. 4 shows a detailed view of the carriage of FIG. 2 in the region ofa rear guiding element; and

FIG. 5 shows a sectional view in accordance with II-II of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 shows the tail-lift in its retracted travelling position, withfolded platform 50, installed on the rear of a trailer 10. The liftingmechanism 30 with platform 50 is connected to the trailer 10 via guidingelements 40 a, 40 b (FIG. 2) in the region FZ and FD using two guidingrails 21. The center of gravity of the net weight of lifting mechanism30 and platform 50 is in the region of FE. This force generates thetractive force in FZ and the compressive force in FD.

In the working position of the tail-lift, shown in broken view, the netweight FE and the useful load FN act on the platform 50, which generatethe largest forces in FZ and FD in this case. During stowage, thelifting mechanism 30 with folded platform 50 is moved into thetravelling position. The support arms and platform 50 remain below thelevel of the rubber buffers 26. The platform 50 is subsequently liftedagainst the rubber buffers 26 using the lifting function to clamp thetail-lift. This increases of course the forces acting in FZ and FD.

FIG. 2 shows part of the support tube 31 with vertical carriage plate 32in the guiding rail 21 shown with dashed lines. The region FZ shows theposition of the guiding element 40 b. In the region FD, the frontguiding element 40 a is supported on the recess 32.5 (FIG. 3) which isopen to the top of the carriage 32. In the region FZ, the rear guidingelement 40 b penetrates through the carriage 32 in the region of theopening 32.3 (FIG. 4). In the region FD, the arrangement and the forcetransmission are analog to FZ, however, with the difference, that therecess 32.5 opens to the top.

FIG. 3 shows the front guiding element 40 a which consists of thesliding member carrier 41 a and the sliding member 42 a which positivelyengage each other. The front sliding member carrier 41 a is looselyattached from above onto the plate-shaped carriage 32, is guided thereonin a vertically displaceable manner and is disposed to be tilted due tosufficient play. Towards this end, the sliding member carrier 41 a hasguiding recesses 41.1 on its front end, which extend over the verticalsurface 32.4 of the carriage 32. The force is transmitted to the slidingmember carrier 41 a in the region FD via the radius-shaped abutmentsurface 32.6 of the recess 32.5 which is convexly curved (radius R) intothe recess 32.5. The forces are transmitted in a planar manner from thesliding member carrier 41 a to the sliding member 42 a and from thesliding member 42 a to the upper sliding path 21.2 (FIG. 5) of theguiding rail 21. The sliding member carrier 41 a, viewed transversely tothe guiding direction of the carriage 32, and the sliding member 42 a,viewed in the guiding direction of the carriage 32, each have a U-shapedcross-section and positively engage each other over their full surfaces.

FIG. 4 shows the rear guiding element 40 b which consists of the slidingmember carrier 41 b and the sliding member 42 b. The rear sliding membercarrier 41 b penetrates through the carriage 32 in the opening 32.3which must be sufficiently large to permit mounting of the slidingmember carrier 41 b including sliding member 42 b. The rear slidingmember carrier 41 b is loosely attached from below onto the plate-shapedcarriage 32 and can be displaced thereon in a vertical direction and canalso be tilted due to sufficient play. Towards this end, the slidingmember carrier 41 b has guiding recesses 41.1 on its front end whichextend over the vertical surface 32.4 of the carriage 32. The force istransmitted to the sliding member carrier 41 b in the region FZ throughthe radius-shaped abutment surface 32.3 of the opening 32.2 which isconvexly curved (radius R) into the opening 32.3. The forces aretransmitted in a planar manner from the sliding member carrier 41 b tothe sliding member 42 b and from the sliding member 42 b to the lowersliding path 21.1 (FIG. 5) of the guiding rail 21. The sliding membercarrier 41 b, viewed transversely to the guiding direction of thecarriage 32, and the sliding member 42 b, viewed in the guidingdirection of the carriage 32, each have a U-shaped cross-section andpositively engage each other over their full surfaces.

FIG. 5 shows a section through the longitudinal carrier 11 of thetrailer 10, the carriage 32 and the guiding rail 21 in the regionbetween FZ and FD. It is clearly shown that the guiding elements 40 a,40 b guide the carriage 32 via the sliding members 42 a, 42 b and thesliding member carrier 41 a, 41 b in a vertical direction on the lowersliding path 21.1 and also on the upper sliding path 21.2. Thehorizontal guidance is obtained by the vertical surfaces of the slidingmembers 42 on the vertical inner surfaces 21.3 of the guiding rail 21.The horizontal guiding forces are transmitted from the sliding member 42to the sliding member carrier 41 through positive engagement of thesetwo parts. The positive connection of the guiding elements 40 and thecarriage 32 is obtained through positive engagement of the guidingrecesses 41.1 which extend over the vertical surface 32.4 (FIGS. 3, 4)of the carriage 32. In the embodiment shown, the two sliding membercarriers 41 a, 41 b and their sliding members 42 a, 42 b have the samedesign.

This carriage guidance requires a minimum number of components whichcannot be reduced. The laser-cut carriage 32 can be connected to thesupport tube 31 through welding. The guiding elements 40 can be easilyinserted due to their positive shape before assembly with the guidingrail 21. The guiding elements 40 connect the lifting mechanism 30 andthe platform 50 to the guiding mechanism 20. The sliding member carriers41 are simple milled parts of normal constructional steel. The carriage32 itself is produced from high-tensile fine-grained steel. The slidingmember 42 is connected to the sliding member carrier 41 also throughpure positive locking in all directions of force without any connectingmeans. The radius-shaped surfaces 32.2, 32.6 in the opening 32.3 and inthe recess 32.5 ensure full-surface abutment of the sliding members 42on the lower sliding path 21.1 and upper sliding path 21.2 throughtilting of the sliding member carriers 41 a, 41 b. Even when the slidingmembers 42 are worn, uniform surface pressure between sliding member 42and the lower sliding path 21.1 and upper sliding path 21.2 is ensured.

If the material has been appropriately selected, e.g. high-tensilefine-grained steel on the carriage 32 and a relatively softconstructional steel on the sliding member carrier 41, the material willflow when the material strength has been exceeded until the surface hasenlarged to a sufficient degree such that the material can adopt theforces. This process occurs in magnitudes of far less than a millimeterand therefore has no effect on the function. The same applies forinaccuracies produced by the support tube 31 and the carriage 32.Deviations from the right angle in the horizontal plane caused byproduction can be compensated for in the same manner.

1. Tail-lift for a vehicle, said tail-lift comprising: a liftingmechanism for lifting and lowering a platform; left and right sideguiding rails on which the lifting mechanism is suspended with a leftplate-shaped vertical carriage depending from the left guiding rail, anda right plate-shaped vertical carriage depending from the right guidingrail, the left and right carriages being slidably displacable between aworking position located behind the vehicle and a traveling positionlocated below the vehicle; left and right front guiding elements eachwith upper sliding members, the left front guiding element beingattached into a recess of the left carriage at a right angle to the leftcarriage and the right front guiding element being attached into arecess of the right carriage at a right angle to the right carriage, therecesses opening to top edges of the left and right carriages; and leftand right rear guiding elements each with lower sliding members, theleft rear guiding element being attached into an opening of the leftcarriage and disposed on the left carriage at a right angle to the leftcarriage and the right rear guiding element being attached into anopening of the right carriage and disposed on the right carriage at aright angle to the right carriage.
 2. Tail-lift according to claim 1,wherein each front guiding element is tiltably disposed and isvertically displaceable with respect to the corresponding carriage. 3.Tail-lift according to claim 2, wherein each carriage comprises anabutment surface cooperating with a sliding member of a correspondingfront guiding element, each abutment surface being convexly curved. 4.Tail-lift according to claim 1, wherein each rear guiding element istiltably disposed in a corresponding carriage opening and is verticallydisplaceable with respect to the corresponding carriage.
 5. Tail-liftaccording to claim 1, wherein each carriage comprises an abutmentsurface cooperating with the sliding member of a corresponding rearguiding element, each abutment surface being convexly curved. 6.Tail-lift according to claim 1, wherein the front and rear guidingelements project beyond both sides of the carriage.
 7. Tail-liftaccording to claim 1, wherein a sliding member of the front and rearguiding elements has a U-shaped cross-section.
 8. Tail-lift according toclaim 7, further comprising front sliding member carriers and rearsliding member carriers each having a U-shaped cross-section, eachsliding member carrier and corresponding sliding member being rotated by90° with respect to one another and abut one another over entiresurfaces thereof.
 9. Tail-lift according to claim 1, further comprisingfront and rear sliding member carriers for holding the upper and lowersliding members respectively.
 10. Tail-lift according to claim 9,wherein the front sliding member carrier and the rear sliding membercarrier each have a U-shaped cross-section and the sliding membercarriers and corresponding sliding members are disposed at 90° withrespect to one another and abut one another over entire surfacesthereof.